This invention relates to electronic control circuitry designed to control bi-directional, or back-and-forth, motion of a driven element. The driving energy is supplied by an electric motor, whose clockwise and counterclockwise motion is controlled. In many instances this rotary motion is converted into reciprocating motion of the driven member by suitable means, such as a lead screw.
One of the important parameters of this invention is the capability of using logic level input voltage and current to develop sufficient power output to operate a motor which exerts substantial driving force.
Another important parameter of this invention is the requirement that motion in one direction be accompanied by "lockout" of an oppositely-acting driving signal which could cause short circuiting.
In some instances, the following truth table will be useful:
______________________________________ A = 0 A = 1 ______________________________________ B = 0 Motor off - breaking Motor on - reverse B = 1 Motor on - forward Motor off - coasting ______________________________________
In other instances, the braking option may be unnecessary, or undesirable.
There are numerous uses for such control systems. The assignee of the present invention has used such control systems in numerous driven-element-positioning machines, as disclosed in Sweeney U.S. Pat. No. 4,353,019, issued Oct. 5, 1982; and in Sweeney application Ser. Nos. 576,013, a continuation-in-part of 289,922, (now abandoned) filed Aug. 4, 1981, and Ser. No. 439,299, filed Nov. 4, 1982. In FIG. 2 of application Ser. No. 576,013 and in FIG. 2 of application Ser. No. 439,299, motor-control circuitry is shown, which is substantially more complex than the present invention, and which is shown receiving signals from "axis interface" circuits interfaced between the motor-control circuitry and the CPU.
There are various other significant uses for improved motor-control circuits of this type. For example, the assignee of the present application has incorporated the circuit of this invention in a medical device of the type which provides continuous passive motion "exercises", such as flexing of a patient's leg.
This control circuitry is designed for use in a digitally-controlled system. The transistors involved in it function in the switch mode, operating essentially in the saturation and cutoff regions. Their amplification is very substantial, but no linearity of amplifier response is required. Variations in the speed, or driving energy, of the controlled motor are accomplished by pulse-width (or pulse-frequency) modulation at the input, i.e., by duty-cycle variations.